Add TrailingWhitespace linter

Closes sds#468

CHANGELOG.md

@@ -13,6 +13,8 @@
   properties
 * Change `NameFormat` to no longer check placeholder names, as this is handled
   by the `SelectorFormat` linter
+* Add `TrailingWhitespace` linter which reports whitespace characters at the
+  end of a line
 
 ## 0.39.0
 

config/default.yml

@@ -184,6 +184,9 @@ linters:
   TrailingSemicolon:
     enabled: true
 
+  TrailingWhitespace:
+    enabled: true
+
   TrailingZero:
     enabled: false
 

lib/scss_lint/linter/README.md

@@ -46,6 +46,7 @@ Below is a list of linters supported by `scss-lint`, ordered alphabetically.
 * [SpaceBetweenParens](#spacebetweenparens)
 * [StringQuotes](#stringquotes)
 * [TrailingSemicolon](#trailingsemicolon)
+* [TrailingWhitespace](#trailingwhitespace)
 * [TrailingZero](#trailingzero)
 * [UnnecessaryMantissa](#unnecessarymantissa)
 * [UnnecessaryParentReference](#unnecessaryparentreference)
@@ -1369,6 +1370,10 @@ CSS allows you to omit the semicolon if the statement is the last statement in
 the rule set. However, this introduces inconsistency and requires anyone adding
 a property after that property to remember to append a semicolon.
 
+## TrailingWhitespace
+
+Reports lines containing trailing whitespace.
+
 ## TrailingZero
 
 Don't write trailing zeros for numeric values with a decimal point.

lib/scss_lint/linter/trailing_whitespace.rb

@@ -0,0 +1,14 @@
+module SCSSLint
+  # Checks for trailing whitespace on a line.
+  class Linter::TrailingWhitespace < Linter
+    include LinterRegistry
+
+    def visit_root(_node)
+      engine.lines.each_with_index do |line, index|
+        next unless line =~ /[ \t]+$/
+
+        add_lint(index + 1, 'Line contains trailing whitespace')
+      end
+    end
+  end
+end

spec/scss_lint/linter/trailing_whitespace_spec.rb

@@ -0,0 +1,33 @@
+require 'spec_helper'
+
+describe SCSSLint::Linter::TrailingWhitespace do
+  context 'when lines contain trailing spaces' do
+    let(:scss) { <<-SCSS }
+      p {
+        margin: 0;\s\s
+      }
+    SCSS
+
+    it { should report_lint line: 2 }
+  end
+
+  context 'when lines contain trailing tabs' do
+    let(:scss) { <<-SCSS }
+      p {
+        margin: 0;\t\t
+      }
+    SCSS
+
+    it { should report_lint line: 2 }
+  end
+
+  context 'when lines does not contain trailing whitespace' do
+    let(:scss) { <<-SCSS }
+      p {
+        margin: 0;
+      }
+    SCSS
+
+    it { should_not report_lint }
+  end
+end